Method of making pre-broken-in papermakers&#39; felt



n 4, 1968 c. G. TEWKSBURY ETAL 3,386,849

METHOD OF MAKING FEE-BROKEN-IN PAPERMAKERS FELT Filed Nov. 29, 1966 I J!ll r,nl'l l I 36 x ATTORNEYS INVENTORS l HA .TEWKSEURY \L LLOU%EEJ.GMIZELL Patented June 4, 1968 3,386,849 METHOD OF MAKINGPRE-BROKEN-IN PAPERMAKERS FELT Charles G. Tewlrsbury, Neenah, Wis., andLouis B. Mizell, Montgomery County, Md., assignors to Appleton Mills,Appleton, Wis., a corporation of Wisconsin Continuation-impart ofapplication Ser. No. 523,493, Dec. 21, 1965. This application Nov. 29,1966, Ser. No. 604,199

6 Claims. (Cl. 117-65.2)

This application is a continuation-in-part of our application Ser. No.523,493, filed Dec. 21, 1965, which in turn is a continuation-in-part ofour application Ser. No. 250,919, filed Jan. 11, 1963, both nowabandoned.

This application relates to improvements in papermakers felts and, inparticular, to a method of making wool or predominantly wool papermakersfelts which have physical characteristics resembling felts that havebeen in operation for substantial period on papermaking machinery.

Papermakers felts are employed in the manufacture of paper to convey afreshly laid web of wet paper after it leaves the forming wire; toconduct the web through the paper finishing presses; and to remove waterfrom the paper in press sections of the machinery. 1

A papermakers felt must have a high degree of dimensional stability,properties permitting the felt to convey or to pick up and retain thewet fibrous paper during the processing thereof and the felt must be ofsufficient porosity to permit rapid removal of water from the freshlylaid sheet. These properties of the felt must be uniform throughout thefelt if the paper produced and finished thereon is to be uniform inquality.

Felts as conventionally constructed and finished do not have uniformfunctional and physical properties and it has been found necessary torun new felts on papermaking machinery at reduced rates of speed forsubstantial periods in order to break the felts in. Because of the highunit cost of papermaking machinery and the substantially reducedproduction capacity of papermaking machines during the break-in period,breaking in of felts has been a comparatively expensive operation forthe papermaking industry.

Tests have shown that during the felt break-in period a felt undergoessubstantial changes in its functional and physical properties and afterthe break-in period, the felt is more or less stable for the duration ofthe felts life. Compared to the same new felts, felts which have beenrun-in and reached comparatively stable conditions, exhibit thefollowing properties: improved water-removability; reduced airpermeability; improved surface finish; reduced thickness; reducedcompressibility; and increased resiliency.

Further tests indicated that subjecting a wool or predominantly woolpapermakers felt to heat and pressure would result in changes in thefunctional and physical properties of the felt resembling the propertiesof felts which have been run in on papermaking machinery. Thus, while itis possible to produce a broken-in finish on a wool or predominantlywool woven felt by subjecting the felt to heat and pressure, because ofthe inherent wet relaxation of wool fibers, the finish is found not tobe durable and, in operation, the felt would tend to bloom or return toits original untreated condition when wet-out after installation on thepapermaking machine.

It has been found that the pre-break-in finish of a wool felt impartedby subjecting the felt to heat and pressure can be renderedsubstantially permanent by curing a partially polymerized heat settablecomposition within the wool fibers while the fabric is under theinfluence of the heat and pressure whereby the fabric will be compressedand set and the wool fibers of the felt held in the artificially inducedrun-in condition.

It is, therefore, a principal object of the present invention to providea woven, or knitted, or needled, or woven and needled, and the like,wool or substantially wool, papermakers felt provided with functionaland physical characteristics whereby the felt may be run atsubstantially full operational speeds as soon as it is installed on apapermaking machine.

A further object is to provide a method of making a papermakers felthaving improved functional and physical properties to thereby eliminateor greatly reduced the normal felt run-in period on a papermakingmachine during which times the machine must be operated at some fractionof its maximum production capacity.

A further object is to provide such an improved papermakers felt havinga durable finish that is resistant to wet relaxation.

These and other objects and advantages are provided in the method ofmaking an improved papermakers felt comprising forming a predominantlywool fabric, incorporating a solution of a polymerizable heat settablecomposition in the fibers of the fabric, subjecting the fabric toindurating conditions to partially polymerize the composition within thewool fibers, compressing the thickness of the woven fabric by subjectingthe fabric simultaneously to heat and pressure and curing thepolymerizable heat settable composition prior to relaxation of thecompressed fabric, thereby to maintain the fabric substantially in thecompressed configuration.

These objects are also provided by a wool or predominantly woolpapermakers felt comprising a heat and pressure compressed fabriccomposed of predominantly wool yarns having incorporated in the fibersof the yarn a polymerized heat settable composition after the fabric hasbeen heat and pressure compressed and prior to relaxation of thecompressed fabric.

The invention will be more particularly described with reference to theillustrative embodiment of the invention diagrammatically showingapparatus suitable for carrying out the finishing of felts constructedin accordance with the teachings of the present invention.

The basic felt structure may comprise a fabric woven from wool yarns, aneedled fabric structure, a woven felt that is subsequently needled, andthe like, and the basic felt structure may have incorporated thereinsynthetic fibers to impart to the fabric improved abrasion resistanceand other improved physical characteristics. Further, the basic fabricstructure may be subjected to conventional wool or predominantly woolfinishing operations such as burling, fulling, singeing, and the like.

Following the finishing of the wool papermakers felt in accordance withconventional felt finishing procedures, there is incorporated in thefibers of the fabric a polymerizable heat settable material such asphenolic-aldehyde resin-forming materials, which resin-forming materialsare subjected to indurating conditions to partially polymerize the resinforming materials within the fibers of the fabric to be treated asopposed to a surface resin application on the fibers. After partialpolymerization of the resin-forming materials within the fibers, thefabric is subjected to heat and pressure to compress the fabric and curethe resin whereby the cured resin will maintain substantially the hotcompressed configuration of the fabric during operation of the felt on apapermaking machine.

Preferably, the process involves impregnating the fabric with a solutionof a phenol and an aldehyde; condensing, that is, partially polymerizingthe phenolic-aldehyde resin within the fibers of the felt and thensubjecting the felt to heat and pressure and curing thephenolic-aldehyde res n while the fabric is in the desired finishedconfiguration and thereby obtain a durable, compressed finish.

The phenols are a class of aromatic hydroxyl derivatives, in which thehydroxyl group is attached directly to a benzene nucleus within themolecular structure. For example, some common phenols and phenol itself,the simplest of the compounds; ortho-, meta-, or paracresol; thymol;carvacrol; ortho-, meta-, or paranitro-phenol; ortho-, meta-, orpara-chlorophenol; picric acid; resorcinol; alphaor beta-naphthol;phloroglucinol; catechol; and hydroquinone.

The aldehydes on the other hand, are a class of oxygen-containingcompounds having the general formula C H O. Some typical aldehydes areformaldehyde, glyoxal, acetaldehyde, propionaldehyde, butyraldehyde,chloral, and benzaldehyde.

Other polymerizable heat settable material which may be used to providea durable, broken-in finish when 'used in combination with hotcompression are:

(1) Acrylonitrile;

(2) Acrylamide and its derivatives;

(3) Acrylic acid and derivatives of acrylic acid, such as methacrylicacid;

(4) Acrylic acid esters, such as methyl acrylate;

(5) Esters of substituted acrylic acids such as methyl methacrylate;

(6) Polyamides, such as the reaction produce of polyamines and acidchlorides (hexamethylenediamine and adipoyl chloride);

(7) Epoxies, such as vinyl cyclohexane dioxide.

The complete break-in treatment for W001 fabrics involves saturation ofthe felt in a bath containing the polymer forming materials, elevationof the bath temperature to cause the chemicals to partially react withinthe fibers, rinsing and extracting, and hot compressing the felt andcuring the polymer-forming material while the felt is in the compressedform.

The effectiveness of the treatment depends on several factors, includingthe type and concentration of the chemi cal used, the pH of the treatingsolutions, the temperature of the treating conditions, and the time oftreatment. In general, the treating conditions should be such that thechemicals will not react or polymerize within the treating bath anddeposit resin on the surface of the fibers, but rather will react at arate so as to allow formation of low molecular weight polymers withinthe fibers themselves.

In general, the treating conditions for a phenolic-aldehyde resintreatment fall within the following ranges:

Treatment variable: Preferred range Phenol concentration 0.02 to 0.5molar. Aldehyde concentration 0.02 to 0.5 molar. Temperature 100 to 200F.

pH 6 to 8.

Time of treatment minutes to 2 hours.

It should be borne in mind that the above treatment is in effect apro-treatment for the hot compression process, and it is desired only toform low molecular weight polymers within the fibers rather than tocompletely polymerize the phenolic-aldehyde in the pre-treating step. Itis not desired to completely cure or polymerize the internal polymeruntil the felt has been compressed and is in its final configuration. Ifthe polymer should completely cure before the felt is hot compressed,then the hot compression step will have little effect on the feltproperties.

Since some of the phenols listed above, such as phloroglucinol andnaphthol, are either insoluble or only slightly soluble in water, it isnecessary to first dissolve them in a solvent such as alcohol and theneither dilute the alcohol solution of the phenol with water to thedesired concentration or use alcohol or an appropriate solvent as thetreating medium.

After treatment with the phenolic-aldehyde solution,

or other treating solution, the felt should be rinsed so as to removeany unreacted chemicals and/or other materials from the surface of thefibers, and preferably extracted to from about 30% to about 100% Wetpickup. The felt, containing the low molecular weight polymer Within itsfibers, may then either be dried at low temperatures, hot compressed,and finally cured in the hot compressed state, or be hot compressedWhile still in the wet state and cured.

One form of apparatus suitable for carrying out the finishing of thefabric is illustrated in the drawings and is generally designated 10.The treating apparatus includes a frame 12 having adjacent its ends apair of rollers 14 and 16. The width of the rolls 14 and 16 should be atleast slightly greater than the width of the fabric to be treated. Oneor both of the rolls 14 and 16 is provided with drive means 18 whichdrive means is preferably of the adjustable speed type whereby the speedof the Web traveling about the pair of rolls 14 and 16 is selectivelycontrollable.

The other of the rolls 16 is mounted in adjusting means generallydesignated 20 whereby the distance between the center of the rolls 14and 16 may be variously adjusted to accommodate different size webs.

The adjusting means 2% includes a motor 34 drivably connected to thespeed reducing means 36 which, in turn, drives a shaft-engaging a rackextending along each side of the frame 12 whereby upon actuation of themotor 34, the frames carrying the idler roll 16 are moved toward or awayfrom the roll 14, depending upon the direction of rotation of the motor34. As illustrated in the drawing, the assembly also includes aconventional stand having adjustably mounted thereon a felt roll 46which maintains the lower flight of the felt A at a predeterminedposition of wrap about the roll 14 which prevents sag in the felt.

The driven roll 14 is provided with heating means which, as illustratedin the drawing, may comprise valved conduit means 46 for directing aheating fluid, such as superheated steam, hot oil, etc., into theinterior of the roll 14 from a source not shown in the drawing.

Positioned vertically above the axis of rotation of roll 1.4 is asupport means 48 which adjustably carries a further roll 59. Theadjusting means generally designated 52 permits the surface of the roll59 to be brought into contact with the surface of the felt A as itpasses over the roll 14 during predetermined periods of treatment of thefelt.

In the illustrated form of the invention, the means for varying thepressure applied to the felt includes a hydraulic ram 54 connected atopposite ends to a source of pressure fluid by conduits 56 and 58 which,in turn, are connected to suitable control valves not shown in thedrawing.

The roll may also be connected to a source of heating fluid throughvalved conduit means generally designated 60 whereby temperature of theroll 50 may also be maintained at a predetermined temperature during aportion of the operation of the press.

In the illustrated form of the invention, the heating and compressingmeans for finishing the felt are metal-tometal rolls; however, it willalso be apparent to those skilled in the art that the heating andcompressing means may comprise a stack of calender rolls such as used inpaper mills.

When the felt is to be saturated in a bath containing the polymerforming material on the same apparatus employed to heat and compress thefelt and polymerize the polymer-forming material, a tank generallydesignated is positioned between the stand 44 and the idler roll 16. Thetank 70 has a width greater than the width of the largest felt to betreated on the apparatus and is provided with a lower pipe connection 72and an upper pipe connection 75. Pipe connection 72 is connected throughsuitable piping 76 to a motor-driven pump generally designated 78. Theother pipe connection 74 is selectively connected by suitable conduitmeans 80 and valve 81 to a storage tank 82 for the treating material orthrough conduit 80, valve 81 and conduit 83 to a drain.

Within the tank 82 may be provided suitable heating means and athermostat for maintaining the temperature of the polymer-formingmaterial where desired. The connection 74 and its conduits 80 and 83provide an overflow drain for the tank 70 whereby the level of the fluidin the tank 70 may be maintained at a predetermined level. The tank 70is also provided with a bottom drain 84 which is connected to a downpipe86 which downpipe is connected to a valve 88. The valve selectivelyconnects the pump 78 or the drain 84 to conduit 90 which has connectionto the storage tank 83. Wash liquid may be directed to the tank 70 froma source not shown via valved inlet 91 and drained from the tank viavalve outlet 93.

A plurality of rolls 92, 94, 96, 96' and 98 control the path of the feltthrough the tank 70 and rolls 92 and 96' also act as extraction rolls toremove a portion of the polymer-forming material picked up in the feltwhen it passes through the polymer-forming bath. Roll 96 is mounted foradjustment toward and away from roll 96 whereby the extraction pressuremay be suitably varied and the roll 94 is removable whereby passage ofthe felt through the tank 70 may be bypassed.

The normal ranges for hot compressing the felts in accordance with theteachings of the present invention are shown in the table below:

Normal range of treating conditions Platen or roll temperature F 200-500Platen or average roll pressure p.s.i 100-300 Dwell time seconds 1-30Polymerization temperature within the felt Under these normal treatingconditions, the heat compressed felt will be 40% to about 70% inthickness compared to the thickness of the fabric in the uncompressedstate.

The above conditions will vary, depending on such factors as the feltcondition, felt construction and thickness, and the like. It will beunderstood that these factors are all interrelated and as one condition,such as temperature is increased, the others will be decreased and viceversa. For example, if the temperature is 300 F., then a pressure of,for example, 100 lbs/square inch can be used. If the temperature isdecreased to, for example, 200 F., it may be necessary to increase thepressure to, for example, 300 lbs/square inchin order to obtain the sameresults in substantially the same period of time.

When pressure rolls are used, the pressure increases from zero as thefelt enters the nip to a maximum at mid-nip and then decreases back tozero as it leaves the nip. For this reason, the pressure in the nip isbest described as an average pressure. This average pressure, expressedin lbs./ square inch, is the weighting or load on the nip, expressed inlbs/inch, divided by the length in inches in the direction of travelover which the weighting force is exerted on the felt.

The dwell time of the felt in the nip of the pressure rolls is governedby the diameter of the rolls and the speed of travel of the felt throughthe rolls. The dwell time employed is dependent upon the temperature ofthe rolls and the pressure between the rolls, and is adjusted so thatthe temperature developed within the felt is 200- 375 F. The rolltemperature may be greater than that developed in the felt up to 500 F.or even higher when the felt is being passed through the rollers at ahigh rate of speed.

Examples 1, 2 and 3 are examples of wool or predominantly wool fabricswhich may be finished in accordance with the teachings of the presentinvention.

Example 1 A plain woven pulp felt was constructed from wool yarns. Thefilling yarns had a weight designation of 3/4 'cut and the warp yarns aweight designation of 2/3 cut. The felt had a thread count of 6 ends perinch and 5 picks .per inch and comprised 100% wool fiber.

Example 2 A cylinder top felt was constructed from 100% wool fiber,using 6 cut worsted warp yarn and 6 cut woolen filling yarn. The feltwas constructed in a 3/1 weave and had a thread count of 13 ends perinch and 18 picks per inch.

Example 3 A C.F. wet grade felt was constructed by mechanicallyinterlocking, in a needle loom, a thick web of randomly arrayed woolfibers into a woven substrate containing by weight of wool fibers and15% by weight of Dacron.

Example 4 An all-woo'l cylinder felt constructed in accordance withExample 2 was ful-led in accordance with conventional fulling practicesand placed on the apparatus illustrated in the drawings.

The storage tank 82 and the felt treating tank 70 were filled with anaqueous solution of 0. 2 molar phenol and 0.2 molar formaldehyde. Thedriven roll 14 was actuated whereby the entire felt was passed throughthe aqueous solution in the tank 70 and then the solution temperaturewas raised to 150 F. No buffers were used to adjust the pH of thetreating bath as it was found that the treating bath had a neutral pH.The felt was continuously passed through the treating bath heated to atemperature of 150 F. for approximately an hour. The solution was thendrained from the tank and excess treating solution extracted from thefelt.

Water was then directed into the tank 70 and the eX- tracted felt Waswashed of excess treating solution. Following the wash the tank wasdrained and the rolls 14 and 50 were then seated to a roll temperatureof approximately 300 F. and the upper roll 50 was lowered to provide apressure of approximately l bs/square inch the roll nip. The felt waspassed through the compression roll until dried.

It was found that the finished felt had a permanently compressed finishwhich was resistant to wet relaxation and which exhibited the propertiesof a broken-in felt.

Example 5 A OF. wet grade felt constructed in accordance with Example 3was treated for one hour in a bath of 0. 15 molar phenol and 0.15 molarformaldehyde. The bath temperature was maintained at F. During thetreatment, the felt was kept in constant motion within the bath.Following the chemical treatment, the felt was removed to a clear waterbath and was thoroughly rinsed after which it was extracted. The wetfelt was placed on apparatus of the type illustrated in the drawing andwas passed through the hot compression ro'lls at a temperature of 300 F.and .a roll pressure of about 100 lbs/square inch. The treated felt wasfound to have greater resilience, less compressibility, improved abilityto extract Water from a wet paper sheet, and stabilized dimensions, thatis, resistance to recovery from compression when wet out, than the sameuntreated compressed felt.

The following are examples of predominantly wool fabrics provided withresin monomers other than phenol and formaldehyde.

Example 6 An all-Wool cylinder tissue felt was treated for 15 minutes inan aqueous solution containing 0.30 molar resorcinol and 0.30 molarformaldehyde at a temperabe satisfactory for hot compression inaccordance with the procedures set forth in Example 4.

Example 7 An all-wool CF. wet felt was treated in an aqueous solution of0.25 molar catechol and 0.25 molar formaldehyde for two hours at atemperature of 140 F. The pH of the treating bath was neutral. Afterrinsing and drying, the felt was found to be satisfactory for hotcompression in accordance with the procedures set forth in Example 4.

Example 8 An all-wool pickup grade felt was treated in a bath comprising0.2 molar phenol and 0.2 molar g'lyoxal at a temperature of 180 'F. ThepH of the bath was neutral and the treating time was 30 minutes. Therinsed and dried felt was satisfactory for hot compression in accordancewith the procedures set forth in Example 4.

Example 9 An all-wool cylinder tissue felt woven from 2/20"s cut pliedworsted warp yarns and v10 cut singles of 51 ends per inch and 47 picksper inch was treated in an aqueous treating solution containing 6% byweight of vinyl cyclohexane dioxide, 1.5% zinc oxide, and 6.4% zincfluoroborate. The wool felt was immersed in the treating solution atroom temperature for 30 minutes, and then was extracted to 40% wetpickup and dried. The dried felt was satisfactory for hot compression inaccordance with the procedures set forth in Example 4.

Examples 10 and 11 show the preparation of prebroken in papermakers feltusing a platen press.

Example 10 The felt used in this example was a fine press allwoolpapermakers felt constructed of 4-cut woolen yarns and woven with 10ends/inch and 16 picks/inch in the loom state. The woven felt wasfinished by conventional means including burling, fulling, washing anddrying.

The finished felt was immersed in a cold aqueous treating solutioncontaining 2% by weight of resorcinol and 1.5% by Weight of formalin.The temperature of the solution was raised to 160 F. and the feltagitated in the heated solution for 30 minutes. The felt was thenremoved from the solution, rinsed thoroughly in lukewarm water andcentrifugally extracted to remove excess moisture. Using an electricallyheated, hydraulically loaded platen press, the indurated felt was hotcompressed at a temperature of 350 F. at a pressure of 227.5 lbs./square inch for a dwell time of 30 seconds.

After standing in a conditioned atmosphere at 70 F. and 65% relativehumidity, the compressed felt was flexible, resilient, relativelyresistant to wet relaxation and had an air permeability of 12c.f.m./square foot. The increase in weight due to the incorporation ofpolymer within the felt was 8%.

Example 11 A felt similar to that used in Example 10 was immersed in acold aqueous treating solution containing 5% by weight of phenol, 3.75%by weight of formalin and 0.2% by weight of sodium carbonate. Thetemperature of the solution was raised to 180 F. and the felt agitatedin the heated solution for 30 minutes. The indurated felt was removedfrom the solution, rinsed, centrifugally extracted and hot compressed asdescribed in the previous example.

After standing in a conditioned atmosphere at 70 F. and 65% relativehumidity, the compressed felt was flexible, resilient, relativelyresistant to wet relaxation and had an air permeability of 7c.f.m./square foot. The increase in weight due to the incorporation ofpolymer within the felt was 4%.

Comparable experiments wherein the same felt was saturgit d but notindurated with treating solution gave,

after hot compression, stiff, glazed and/or filled felts unsuitable foruse as papermakers felts.

From the foregoing disclosure, it will be seen that the process of thisinvention provides a method of producing papermakers felts having adurable compressed, brokenin finish with additional benefits of enhancedabrasion resistance, chemical resistance, dimensional stability andother improved functional properties.

We claim:

1. A method of making a pre-broken-in papermakers felt from apredominately wool fabric which comprises indurating the fabric with anaqueous solution of a polymerizable heat settable composition topartially polymerize the composition within the fibers of the fabric,rinsing the indurated fabric, to remove heat settable composition fromthe surface of the fibers, and then heat curing the partiallypolymerized composition within the fibers of the fabric at a temperaturebetween about 200 to 375 F. while maintaining the fabric in a compressedconfiguration between coacting pressure members at a pressure betweenabout to 300 lbs/square inch thereby fixing the fabric substantially inthe compressed configuration.

2. A method according to claim 1 which comprises indurating the fabricat a pH between about 6 to 8 for about 15 to minutes with a 0.02 to 0.5molar aqueous solution of a phenol and an aldehyde to partiallypolymerize the phenol and aldehyde composition within the fibers of thefabric, rinsing the indurated fabric, to remove phenol and aldehydecomposition from the surface of the fibers, and then heat curing thepartially polymerized composition within the fibers of the fabric at atemperature between about 200 to 375 F. while maintaining the fabric ina compressed configuration between coacting pressure members at apressure between about 100 to 300 lbs./ square inch thereby fixing thefabric substantially in the compressed configuration.

3. A method of making a pre-broken-in papermakers felt from apredominately wool fabric which comprises indurating the fabric with anaqueous solution of a polymerizable heat settable composition topartially polymerize the composition within the fibers of the fabric,rinsing the indurated fabric, to remove heat settable composition fromthe surface of the fibers, and then passing the rinsed and induratedfabric at a temperature of 200375 F. through the nip of coactingpressure rolls exerting an average pressure of 100-300 lbs/square inchon the fabric a sufiicient number of times to cure the heat settablecomposition and fix the fabric in the compressed configuration.

4. A method according to claim 3 which comprises indurating the fabricwith a 0.02 to 0.5 molar aqueous solution of a phenol and an aldehyde topartially polymerize the phenol and aldehyde composition within thefibers of the fabric, rinsing the indurated fabric, to remove phenol andaldehyde composition from the surface of the fibers, and then passingthe rinsed and indurated fabric at a temperature of 200-375 F. throughthe nip of coacting pressure rolls exerting an average pressure of100-300 lbs/square inch on the fabric a sufficient number of times tocure the phenol-aldehyde composition and fix the fabric in thecompressed configuration.

5. A method according to claim 3 which comprises indurating the fabricat a pH between about 6 to 8 for about 15 to 120 minutes with a 0.02 to0.5 molar aqueous solution of a phenol and an aldehyde to partiallypolymerize the phenol and aldehyde composition within the fibers of thefabric, rinsing the indurated fabric, to remove phenol and aldehydecomposition from the surface of the fibers, and then passing the rinsedand indurated fabric at a temperature of 200-375 F. through the nip ofcoacting pressure rolls exerting an average pressure of 100-300lbs/square inch on the fabric a sufficient number of times to cure theheat settable composition and fix the fabric in the compressedconfiguration.

9 10 6. A method according to claim 5 wherein the phenol 2,589,7653/1952 Berlund 117140 and aldehyde composition comprises phenol andformal- 3 075 274 1 19 3 i n 2 74 dehyde.

References Cited FOREIGN PATENTS UNITED STATES PATENTS 5 650,190 10/1962 Canada.

2,503,629 4/1950 Miscall 117140 2,545,450 3/1951 Dalton et a1. 117 141MURRAY KATZ, Primary Examl'wr-

1. A METHOD OF MAKING A PRE-BROKEN-IN PAPERMAKERS'' FELT FROM APREDOMINATELY WOOL FABRIC WHICH COMPRISES INDURATING THE FABRIC WITH ANAQUEOUS SOLUTION OF A POLYMERIZABLE HEAT SETTABLE COMPOSITION TOPARTIALLY POLYMERIZE THE COMPOSITION WITHIN THE FIBERS OF THE FABRIC,RINSING THE INDURATED FABRIC, TO REMOVE HEAT SETTABLE COMPOSITION FROMTHE SURFACE OF THE FIBERS, AND THEN HEAT CURING THE PARTIALLYPOLYMERIZED COMPOSITION WITHIN THE FIBERS OF THE FABRIC AT A TEMPERATUREBETWEEN ABOUT 200 TO 375*F. WHILE MAINTAINING THE FABRIC IN A COMPRESSEDCONFIGURATION BETWEEN COACTING PRESSURE MEMBERS AT A PRESSURE BETWEENABOUT 100 TO 300 LBS./SQUARE INCH THEREBY FIXING THE FABRICSUBSTANTIALLY IN THE COMPRESSED CONFIGURATION.